Process and arrangement for supplying lubricant to a reciprocating piston engine

ABSTRACT

A process and an assembly for supplying a liquid lubricant to points of a reciprocating piston engine which are to be lubricated and which include at least running surfaces of a piston-cylinder tube unit of the reciprocating piston engine. The reciprocating piston engine has a piston and a cylinder. According to the process, the lubricant in at least one conditioning device is united with a gaseous transport medium. In the conditioning device, a lubricating mixture is formed including small liquid particles of lubricant carried by the gaseous transport medium. At least one of the lubricating mixture and the lubricant is passed with the gaseous transport medium through a plurality of supply ducts corresponding to the points to be lubricated. The gaseous transport medium and excess lubricant are drawn away through at least one drain disposed in a region of the points to be lubricated.

FIELD OF THE INVENTION

The invention relates to a process and arrangement for supplying aliquid lubricant to the points to be lubricated of a reciprocatingpiston engine, in particular the running surfaces of the piston/cylindertube unit. In particular, the invention relates to supplying lubricantto internal combustion engines, so that while reciprocating pistonengines will be predominantly discussed hereinafter, this in no wayrestricts the invention.

BACKGROUND OF THE INVENTION

Lubricating the points to be lubricated in a reciprocating pistonengine, for instance a four-stroke engine, is done as a rule bypressure-recirculation lubrication, in which the lubricating oil iscarried from a reservoir to the various points to be lubricated via apump and distribution lines. The bearings between the connecting rod andthe crankshaft on the one hand and between the crankshaft and the engineblock on the other are supplied with lubricating oil via correspondingbores in the crankshaft and crankcase, while the lubrication of thepiston/cylinder tube units is done through the injection oil present inthe crankcase. Lubricating the piston/cylinder tube unit by means ofinjection oil has the disadvantage that as a rule substantially morelubricating oil than necessary is delivered to the point to belubricated. Oil stripper rings must therefore be provided, whichincrease the friction between the cylinder and the cylinder tube andthus lower the efficiency of the engine.

In two-stroke internal combustion engines, besidespressure-recirculation lubrication with external scavenging processes,mixture lubrication, especially with crankcase scavenging, is employed.In this lubrication system, the lubricating oil is exposed to the fuel.Together with the fuel, the lubrication oil is atomized and reaches thepoints to be lubricated along with the air aspirated by the engine. Onedisadvantage of this lubricating system is that the lubricant can bedelivered to the various points to be lubricated only in an uncontrolledfashion. There is also the disadvantage that by far the majority of thelubricant exposed to the fuel is expelled again, via the combustionchamber of the engine, without contributing to lubricating the points tobe lubricated. Hence this lubrication system requires increasedconsumption of lubricant and results in major environmental pollution.

It is also known in two-stroke internal combustion engines to deliverthe lubricating oil as a function of engine load and/or engine speed. Inthis so-called separate lubricating system, the delivery of oil,depending on the engine model, is made to the fuel, to the aspiratedair, or directly to the points to be lubricated via liquid pressure oil.With this lubricating system, accurate dosing of the delivered quantityof lubricating oil is impossible, or can be done only with major effort.It is therefore known to deliver the lubricating oil to the point to belubricated in increments, or in other words at time intervals. That hasthe disadvantage, however, that good lubricating action or even excesslubrication is attained only after the delivery of lubricant, and by thenext time lubricant is delivered the lubrication decreases sharply.Since very slight quantities of lubricant are often all that isnecessary, it is impossible with this lubricating system to achieve aprecisely dosed delivery of lubricant.

One process for targeted delivery of lubricant in a two-stroke internalcombustion engine is known from H. W. Bonsch, Der schnell laufendeZweitakt-Motor [The High-Speed Two-Stroke Engine] Motor Buch Verlag1982, page 140, in which each piston/cylinder tube unit is supplied bymeans of pressure oil via a bore. The crankshaft bearing for eachcylinder is likewise lubricated via pressure oil. Another process ofsupplying lubricant to crankshaft bearings is disclosed in SAE Paper85157, published in 1985. In this process, the lubricant is drawn intothe respective bearings by negative pressure via riser lines. For thesake of assuring reliable lubrication provision is also made to blow airinto the riser line by means of the excess pressure in the pistonhousing. In this process, precise dosing of the quantities of lubricantneeded at the various points to be lubricated is not possible.

The object of the invention is to create a process for supplying thepoints to be lubricated in a reciprocating piston engine, with which anat least approximately exactly dosed, targeted delivery of lubricant ispossible.

SUMMARY OF THE INVENTION

The object of the invention is obtained in accordance with the inventionin that the lubricant is united in at least one conditioning device witha gaseous transport medium, forming a lubricating mixture; thelubricating mixture is passed through supply ducts into the region ofthe point to be lubricated; and the lubricant is applied to the surfacesto be lubricated in the form of small liquid particles. This has theadvantage that the lubricant is present, at least in the region of thepoint to be lubricated, finely and uniformly distributed in thetransport medium, forming a lubricant mist or aerosol that uniformlymoistens the point to be lubricated. The transport of lubricant can takeplace via supply lines and/or supply bores embodied as thin tubes. Thetransport of lubricant into these supply ducts can also be in the formof a wall film, and the atomization is effected for instance by across-sectional constriction of the supply duct in the immediatevicinity of the point to be lubricated.

Using this kind of lubricant mixture also has the advantage that it iseasy to deliver and to dose. It also avoids plugging up of the supplyducts from contaminants in the lubricant. In particular, it is evenpossible to deliver merely slight quantities of lubricant that areneeded for the lubricating action, in a simple way. Another advantage isthat this lubricant mixture can also reach regions of the point to belubricated that are located farther away from the outlet opening of thesupply duct.

In accordance with one embodiment of the invention, it is provided thatthe lubricant mixture is split into partial streams, and that thevarious doses for the various points to be lubricated are effected bymeans of suitable flow resistances in the various supply ducts for thepartial streams. It may also be provided that the lubricant and thetransport medium each be mixed in a plurality of conditioning devices,in accordance with the needs of the points to be lubricated that areeach connected to the respective conditioning devices. As a result,individual dosing of the various points to be lubricated can beattained.

The delivery of lubricant mixture to the points to be lubricated issuitably effected continuously. It may be provided in this respect thatthe dosing is effected by varying the volumetric flow of transportmedium and/or the concentration of lubricant in the transport medium.However, it may also be provided that the dosing is effected byintermittent interruption of the volumetric flow of the transport mediumand/or of the volumetric flow of the lubricant stream. Overall, it ispractical that the dosing is effected as a function of the load and/orrpm of the reciprocating piston engine.

A special problem in lubricating reciprocating piston engines islubricating the running surfaces of the piston/cylinder tube unit. Tosupply this point to be lubricated, the invention provides that thelubricant mixture is carried through at least one supply bore in thecylinder wall into the interstice between the outer surface of thepiston and the inner surface of the cylinder wall, and the supply boredischarges into the interstice, in the bottom dead center position ofthe piston, below the uppermost piston ring. This assures that thelubricant mixture for the most part bathes the piston, and the lubricantfor the most part moistens this region of the outer surface of thepiston and the inner surface of the cylinder wall. As a result, it canadvantageously be assured that even if an only slight quantity oflubricant is used, adequate lubricating action is attained. The gaseoustransport medium can flow out through the gap between the piston and thecylinder wall into the crankcase in the course of the upward motion ofthe piston.

To avoid misunderstanding, it is noted here that the lubricant mixturenaturally varies its composition in the course of delivery anddistribution. It is also understood that the gaseous transport mediumdrawn away or draining away may still be laden with lubricants. The termlubricant mixture is therefore employed hereinafter for a volumetricflow flowing to the points to be lubricated or the regions thereof,while the term gaseous transport medium predominantly means thevolumetric flow leaving the point to be lubricated.

For uniform distribution of the lubricant on the surface of the pistonor the cylinder wall, a plurality of such supply bores may be disposedalong the circumference of the cylinder tube. It may also be practicalfor the cylinder wall to have at least one bore for draining away thegaseous transport medium and/or for excess lubricant. This is especiallypractical if the supply bore discharges in a region of the cylinder wallthat is located between two piston rings, in the bottom dead centerposition of the piston. As a result, a satisfactory drainage of thegaseous transport medium can be effected. The bore for removing thegaseous transport medium may be located in the immediate vicinity of thesupply bore, or for instance opposite the some. In the latter case inparticular, adequate bathing of the piston is assured. It is practicalin this respect that the outflow cross section is larger than the inflowcross section.

To improve the distribution of the lubricant mixture in the intersticebetween the piston and the cylinder wall, it may be provided that themouth of the supply or drainage bore into the interstice be widened toform a groove. A groove may also be made in the piston, and itpreferably cooperates, at bottom dead center of the piston, with themouth of the supply bore in the cylinder wall. The grooves disposed onthe outer surface of the piston and/or cylinder wall may by way ofexample extend over at least a portion of the circumference of thepiston or cylinder wall, respectively. It is also possible for thegrooves to extend parallel to the piston axis. Moreover, the groovesdisposed on the outer surface of the piston or cylinder wall may beembodied in the form of a V or an X, for instance. The angle ofinclination of the groove axes relative to the cylinder axis may be 45°,for instance. The advantage of this kind of groove arrangement is thatthe piston ring enters the groove and leaves the groove at selectedpoints. Such a groove also extends not as far in the circumferentialdirection as a horizontal groove would, so that the piston ring isunable to plunge far into the groove. As a result, wear can be reducedconsiderably.

By providing such grooves, the outflow cross section for the gaseoustransport medium can be enlarged, and an increased delivery of lubricantmist can be made possible. It may be advantageous if the grooves areembodied as approximately wedge-shaped in cross section, which promotesthe development of a hydrodynamic lubricant film in the region of thetransition from the widened portion to the cylinder tube wall. It alsohas the effect that the lubricant particles can be carried into the gapto be lubricated along with the outflowing transport medium.

For improved distribution of the lubricant mixture it may be providedthat a plurality of such supply bores and/or drainage bores are disposedalong the circumference of the cylinder wall, with suitable groovegeometries. In a feature of the invention, it is also possible for thebore to discharge into an encompassing groove of the cylinder wall whichat bottom dead center of the piston is located below the lowermostpiston ring. It may also be practical if the bore cooperates with atleast one partially encompassing groove on the outer surface of thepiston. As a result of these provisions, distribution of the lubricantto the appropriate surfaces in a way that is uniform and adapted torequirements can be accomplished. It may be practical in this respectfor the groove to extend helically over the surface of the piston. Oneend of the groove may then terminate in the upper region of the pistonin an encompassing groove, while the other end is open in the directionof the crankcase. This assures an unhindered outflow of the gaseoustransport medium. It may also be practical to provide a plurality ofsuch grooves on the outer surface of the piston.

In another practical feature of the invention it is provided that thelubricant mixture is supplied to the upper connecting rod bearingthrough at least one bore in the piston, which bore cooperates with thesupply bore in the cylinder wall. Thus in an advantageous way, atargeted and dosed lubrication of the upper connecting rod bearing,which by way of example has a roller bearing, can be accomplished. Thebore in the piston may cooperate either directly with the supply bore orindirectly with the supply bore, via grooves disposed in the cylinderwall or via the grooves on the outer surface of the piston. It may beprovided that for supplying lubricant to the upper connecting rodbearing, the grooves on the piston surface terminate on one end at thepiston pin boss. The other end of each groove terminates on the outersurface of the piston, to prevent any possible outflow of lubricantmixture to the crankcase. As a result, a lubricant-containing atmosphereis established in the piston pin, which by way of example is drilled tomake it hollow. Through suitable radial bores in the piston pin, thelubricant mixture can flow out via the upper connecting rod bearing,which assures the supply of lubricant to the bearing. In this respect itmay be practical for the grooves to be disposed helically on the surfaceof the piston, with one end of each discharging into a radial bore thatcommunicates with the connecting rod bearing, while the other endterminates on the piston surface, so that an adequate supply oflubricant to the upper connecting rod bearing is assured.

It is naturally also possible that with the above process the otherpoints to be lubricated in a reciprocating piston engine can also besupplied with lubricant such as the bearings of the crankshaft in thecrankcase. The lubrication of the bearings of the connecting rods on thecrankshaft can take place through corresponding bores in the crankshaft.It may also be provided that the lubricant be carried through acorresponding bore in the connecting rod bearing on the crankshaft and acorresponding bore in the connecting rod to the upper connecting rodbearing.

It may be practical for the lubricant mixture to be delivered to thevarious points to be lubricated under pressure. An external compressormay be provided for that purpose. The excess pressure prevailing in thecrankcase or in the work chamber of the reciprocating piston engine mayalso be utilized for that purpose. The gaseous transport medium and/orthe excess lubricant is suitably drained away from the point to belubricated by the application of a negative pressure to thecorresponding drainage bores. In this course of the process, namelysupplying the lubricant-containing transport medium under pressure onthe one hand and drawing off the gaseous transport medium, optionallywith excess lubricant, by means of negative pressure on the other, it ispossible to supply roller bearings, for instance, with lubricantadequately and in targeted fashion.

This process can especially advantageously be used to supply two-strokeengines, since the requisite consumption of lubricant can thus bereduced considerably. It can also be practical, for assuring thefunctional reliability of the lubricating system at low temperatures, toheat the lubricant and/or the gaseous transport medium inside thelubricant conditioning device and/or the transport lines. In continuousoperation, it may also be practical to cool the volumetric flow oftransport medium or lubricant.

BRIEF DESCRIPTION OF THE DRAWING

The invention will now be described in detail, in conjunction with thedrawing. Shown are:

FIG. 1, a schematic illustration of a reciprocating piston engine withlubricant supply in accordance with the invention;

FIG. 2, in section and on a larger scale, the lubricant supply in theinterstice between the cylinder wall and a piston of a cylinder/cylindertube unit;

FIG. 3, in section, another embodiment of the lubricant supply;

FIG. 4, a section taken along the line IV--IV of FIG. 3;

FIG. 5, the view in the direction of the arrow V of FIG. 3, but withouta piston;

FIG. 6, another embodiment of the lubricant supply;

FIG. 7, in section, the lubricant supply for the upper connecting rodbearing;

FIG. 8, another embodiment of the lubricant supply for the upperconnecting rod bearing;

FIG. 9, in section, the lubricant supply for a roller bearing;

FIG. 10, in section, another embodiment of a lubricant supply to a gapto be lubricated;

FIG. 11, the lubricant supply in the form of wall film transport;

FIG. 12, the elevation view of one version of a groove in a cylinderwall or on the piston;

FIG. 13, the elevation view of a different version of a groove in thecylinder wall or on the piston;

FIG. 14, another groove version, shown on a developed view of the outerpiston surface, with the piston at top dead center and with theassociated cylinder wall shown in suggested form;

FIG. 15, the groove version of FIG. 14 in a middle piston position;

FIG. 16, a modification of the groove version of FIG. 14, with thepiston at top dead center;

FIG. 17, the groove version of FIG. 16 in a middle piston position;

FIG. 18, an embodiment for producing and supplying the lubricantmixture;

FIG. 19, a schematic illustration of a lubricant supply for a two-strokeinternal combustion engine.

DETAILED DESCRIPTION OF THE INVENTION

The lubricating process shown schematically in FIG. 1 for use withreciprocating piston engines has a conditioning device 1 for thelubricant mixture, transport lines 2 to the points to be lubricated inthe reciprocating piston engine 6, and a line 3 for returning unusedlubricant. The conditioning device 1 is provided with one connection 4,5 each for the gaseous transport medium and for the liquid lubricant,respectively, and one connection for the return line 3. Furnishing ofthe gaseous transport medium, such as air, is done through an externalcompressor, not shown in the drawing, or by compressing in the crankcaseor in the work chamber of the reciprocating piston engine. The liquidlubricant can for instance be drawn from a reservoir, not shown in thedrawing.

In the conditioning device 1, the liquid lubricant is combined with thegaseous transport medium, forming a lubricant mixture. Provision mayalso be made so that the returned lubricant will be cleaned andoptionally added to the gaseous transport medium with the addition offresh lubricant. The lubricant mixture passes through the transportlines 2, which are preferably embodied as thin tubes and/or thin bores,to reach the various points to be lubricated.

The transporting of the liquid lubricant by means of the gaseoustransport medium may be done by various mechanisms. One possibletransport mechanism is atomizing the lubricant into small droplets,which are carried where they are needed by the gaseous transport medium.The droplets have a size on the order of magnitude of approximately 1μm. In this transport mechanism, it must be assured, by embodying theend of the transport lines and/or bores toward the lubricant point in aspecial way, that the droplets will be deposited on the points to belubricated. This can be done for instance by increasing the flow speedvia a cross-sectional constriction and by an ensuing deflection of thestream to assure that the heavier lubricant droplets will be depositedon the surface to be lubricated. Another option for causing thedeposition of the lubricant particles is to make a cross-sectionalconstriction, immediately upstream of the point to be lubricated, in theform of a porous body, for instance of gas-permeable ceramic; insidethis cross-sectional constriction, major flow deflections result,leading to a growth in droplet size. These larger droplets can bedeposited without difficulty at the point to be lubricated, because oftheir inertia.

In another transport mechanism, shown in FIG. 11, inside the transportlines 2 a wall film 41 of lubricant is formed, which is entrained by thegaseous transport medium 42 flowing through the lines. The atomizationof the liquid wall film into droplets takes place here by means of across-sectional constriction 43 immediately upstream of or in theimmediate vicinity of the point to be lubricated. Droplets 44 because oftheir size and inertia can deposit on the surface to be lubricated. Bysuitably embodying the end 45 of the cross-sectional constriction towardthe inner surface 26 of the cylinder wall 8, for instance by rounding itoff, the development of a wall film 46 of lubricant on the wall on thesupply side of the point to be lubricated can be attained.

In the exemplary embodiment shown in FIG. 1, the points to be lubricatedin the reciprocating piston engine are supplied with the lubricantmixture by means of a single conditioning device 1. Since as a rule thevarious points to be lubricated have different requirements in terms oflubricants, it may be suitable for the various transport lines to havedifferent flow resistances or different, calibrated outlet openingsand/or bores so that the total volumetric flow can be split up asneeded, and so that every point to be lubricated can be supplied withthe particular amount of lubricant it needs. Moreover, it is alsopossible for a plurality of conditioning devices to be provided, each ofwhich supplies certain points to be lubricated in the reciprocatingpiston engine.

In the reciprocating piston engine 6, lubricant must be supplied inparticular to the main crankshaft bearings 17, the crankshaft connectingrod bearings 19 and the running surfaces of the piston/cylinder tubeunit 21, as well as the upper connecting rod bearing 23 in the piston 7.The supply to the main crankshaft bearings 17 may be done via transportlines and corresponding bores in the engine block 18. The crankshaftconnecting rod bearings 19 can be supplied with lubricant via suitablebores inside the crankshaft 20.

FIG. 2 shows one possibility of supplying lubricant to thepiston/cylinder tube unit 21. The cylinder wall 8 has one or more supplybores 10, distributed over its circumference, which that discharge intothe interstice 11 between the piston 7 and the cylinder wall 8.Advantageously, these bores 10 are disposed in a region of the cylinderwall that is always covered by the piston 7 during its reciprocatingmotion. To avoid losses of lubricant to the combustion chamber 12, thebores 10 are arranged such that in the bottom dead center position ofthe piston 7, they are located below the uppermost piston ring 9. Thispiston position is shown in FIG. 2. The lubricant mixture flows via thebore 10 into the gap (11) between the piston 7 and the cylinder wall 8and bathes the entire piston. In the process, the droplets of lubricantwill deposit on the outer surface 25 of the piston 7 and the innersurface (26) of the cylinder wall 8 and form the lubricant film requiredfor lubricating the running surfaces. The gaseous transport medium canthen flow out via the gap 11 between the piston 7 and the cylinder wall8. For that purpose it may be suitable to provide a groove in thecylinder wall 8, in order to circumvent the lower piston rings 49.

In general the piston 7 has a plurality of piston rings, which restsealingly on the cylinder wall 8. To assure adequate bathing of thepiston including in the region of the piston rings, it may be practicalfor the cylinder wall, in the region of the supply bores, likewise tohave bores for the outflow of the gaseous transport medium. This assuresthat the gaseous transport medium can flow out even if it is carriedinto the annular space defined by the piston rings. Enough lubricant isthen entrained, and in this region can be deposited on the outer surface25 of the piston 7 and the inner surface 26 of the cylinder wall 8, sothat the film of lubricant required for the lubrication can be built upthere. The cross section of the outflow bores should be larger than thecross section of the supply bores.

FIGS. 3-5 show another embodiment for supplying the lubricant-containingtransport medium to the interstice 11 of the piston/cylinder tube unit21. Here the supply bore 10 discharges into a groove 13 that extends atleast partway over the circumference of the cylinder wall 8. By thismeans, the outflow cross section for the gaseous transport medium can beenlarged. The cross section of the groove is preferably approximatelywedge-shaped, which reinforces the buildup of a hydrodynamic lubricantfilm on the top 14 or underside 15 of the groove as a function of thepiston motion. In the exemplary embodiment shown in FIGS. 3-5, thegroove 13 is oriented transversely to the piston motion, and in thecircumferential direction of the cylinder wall 8 it has an essentiallyoval shape. As needed, it may be appropriate for the groove to extend atleast partly parallel to the piston motion.

The groove 13 shown in FIG. 3 may also extend over the entirecircumference of the cylinder wall 8. It is then practical for aplurality of supply bores 10 to be provided. In this embodiment with anencompassing groove, care must be taken that in the bottom dead centerposition of the piston 7, the groove is located below the lowermostpiston ring. It may also be practical for one or more bores to dischargeinto the encompassing groove, in order to carry away the gaseoustransport medium.

In principle, in internal combustion engines and in particularfour-stroke engines, the supply bores 10 can discharge at arbitrarypoints of the circumference into the cylinder wall below the uppermostpiston ring 9 in the bottom dead center position of the piston 7. It ispractical to dispose them in the load-bearing zones, or in other wordson the compression side and counterpressure side of the piston 7. Intwo-stroke internal combustion engines with inlet and outlet slits, itis practical to dispose the supply bores 10 in the circumferentialdirection between the inlet and the outlet slit of the combustionchamber and below the uppermost piston ring 9 in the bottom dead centerposition of the piston. In the bottom dead center position of the piston7, the supply bore 10 is suitably located as directly as possiblebeneath the uppermost piston ring 9, so that the largest possibleportion of the outer piston surface 25 will be supplied with lubricantin the course of the upward motion of the piston 7. Moreover, aplurality of supply bores may also be provided, spaced apart from oneanother parallel to the cylinder axis.

Another option for supplying lubricant to the running surfaces of thepiston/cylinder tube unit 21 is shown in FIG. 6. Here the piston 7 hashelical grooves 16 on its outer surface 25, as a result of which gooddistribution of the lubricant mixture and hence of the lubricant on thepiston circumference is attained. In the exemplary embodiment shown inFIG. 6, the grooves end on the underside of the piston 7, and as aresult the unhindered outflow of gaseous transport medium to thecrankcase can be assured. The angle of inclination α of the helicalgroove 16 must be chosen to meet requirements. Provision may also bemade so that one or more encompassing grooves are disposed on the outersurface of the piston 7 and cooperate with the supply bore 10. By thismeans as well, good distribution of the lubricant over the pistoncircumference can be brought about, and the gaseous transport medium canflow out through the gap 11 between the piston 7 and the cylinder wall8. The grooves 16 suitably cooperate with the supply bore 10 in thebottom dead center position of the piston 7.

Other embodiments of such grooves disposed on the outer surface 25 ofthe piston 7 and/or the inner surface 26 of the cylinder wall 8 areshown in FIGS. 12 and 13. The grooves 48, 47 may be V-shaped (FIG. 13)or X-shaped (FIG. 12). The angle of inclination β of the groove axesrelative to the cylinder axis may be approximately 45°, for instance.The advantage of this kind of groove arrangement in the cylinder tube isthat the piston rings enter the groove and leave the groove at selectedpoints. The groove also extends not as far in the circumferentialdirection as a horizontal groove would, so that the piston ring cannotplunge far into the groove. Provision can also be made for the grooves16, 27, 47, 48 to have a cross-sectional dimension that is equal to oronly slightly larger than the cross section of the supply bore 10.

In FIGS. 7 and 8, options for supplying lubricant to the upperconnecting rod bearing 23 are shown. In the exemplary embodiment shownin FIG. 7, the piston 7 has at least one essentially radially extendingbore 24 in its upper region, which communicates at one end in the outersurface 25 of the piston 7. The mouth of the bore 24 is advantageouslyoffset in the circumferential direction, for example at right angles tothe piston pin 30. The other end of the bore 24 is aimed at the upperconnecting rod bearing 23, which in the exemplary embodiment shown inthe drawing is embodied as a roller bearing. The bore 24 cooperates withthe supply bore 10 disposed in the cylinder wall 8. It is a practicalfeature that the supply of lubricant mixture to the bore 24 takes placein the bottom dead center position of the piston 7, because the piston 7remains there for a relatively long period. It can also be practical forat least the mouth of the bore 24 on the outer surface 25 of the piston7 to have a larger diameter than the supply bore 10, in order to assurethat enough lubricant will be supplied to the upper connecting rodbearing 23. It can likewise be practical for the bore 24 to dischargeinto a groove extending parallel to the piston motion, so that thesupply of lubricant over a certain portion of the motion of the piston 7is assured. For the sake of simplicity, the drawing shows the bore 24and the supply bore 10 offset circumferentially in the plane of thepiston pin 30.

FIG. 8 shows another option for supplying the upper connecting rodbearing 23 with lubricant. In this embodiment, helical grooves 27 aredisposed on the outer surface 25 of the piston 7. The grooves 27 endwith one end at the piston pin boss 28. The other ends 29 of the grooves27 terminate on the outer surface 25 of the piston 7, to prevent anypossible outflow of lubricant mixture to the crankcase. By providing asuitable radial bore in the piston pin 30 it can be assured that thetransport medium, which is at least partly still laden with liquidlubricant, will be carried to the upper connecting rod bearing 23. Thisamount of lubricant is adequate to lubricate to upper connecting rodbearing 23. In a practical way, the grooves 27 cooperate with the supplybore 10 in the bottom dead center position of the piston 7.

FIG. 9 illustrates the possibility of supplying lubricant to a rollerbearing. Roller bearings are often used for the main crankshaft bearingand the crankshaft connecting rod bearing in two-stroke internalcombustion engines. The arrangement for lubricant supply has a supplyline 31, which ends with its outlet opening 32 in the region between theouter and inner race 33 and 34, respectively, of the roller bearing 35.The lubricant mixture, supplied under pressure, reaches the rollerbodies 36. The lubricant that does not deposit there is caught via asuction line 37 disposed on the other side of the roller bearing 37.This assures that excess lubricant can be returned directly to thelubricant conditioning means, without first entering the crankcase, forinstance.

Advantageously, the aspiration line is acted upon by negative pressure.Such aspiration lines can also be disposed for instance in the immediatevicinity of a supply bore 10 for the lubricant-containing transportmedium. In FIG. 10, the supply bore 10 is disposed between twoaspiration lines 38. When the lubricant mixture arrives at the surface39, a certain proportion of the lubricant will be deposited there, whilea certain portion will be deposited inside the lubrication gap 40 bymeans of the transport medium and moisten the surface 39 over a largearea, while the excess amount of lubricant is carried away together withthe gaseous transport medium through the aspiration lines 38. Once againit can be practical for the aspiration lines 38 to be acted upon bynegative pressure. In addition to the provision of a plurality ofseparate aspiration lines, a concentric ring line may also be provided.

It is evident that with this lubrication system, a targeted lubricantsupply with a simultaneously low consumption of lubricant is achieved.In particular, the critical points to be lubricated, namely the runningsurfaces of the piston/cylinder tube unit on the one hand and the upperconnecting rod bearing on the other--for instance in an internalcombustion engine--are supplied in a target way and adequately withlubricants. Moreover, the use of this lubrication system is alsoespecially advantageous in two-stroke internal combustion engines withcrankcase scavenging.

FIG. 14 shows a further exemplary embodiment for the groove, in adeveloped view of the outer surface of the piston (solid line),specifically in its relationship with the associated cylinder wall face8 (dashed lines), at top dead center for a two-stroke internalcombustion engine. The location of the piston pin 30 is suggested withreference to the outer piston surface 25.

As the developed view of the outer piston surface 25 in FIG. 14 shows,one groove 50 is disposed on each of the two surface regions locatedbetween the piston pins; each groove essentially comprises an axialgroove portion 50.1 beginning at the lower piston end, a groove portion50.2 radially offset from it in the upper piston region, and anadjoining groove portion 50.3 extending circumferentially about thepiston. Adjoining this then, the circumferentially extending grooveportion 50.3 merges with a groove portion 50.4 that is again axiallyaligned with the lower piston end, and this portion is in turn adjoinedby a through bore 51 by way of which the groove portion 50.4communicates with the piston pin bearing.

Two diametrically opposed supply bores 10 are disposed in the cylinderwall 8; in the top dead center position of the piston shown in FIG. 14,they discharge into the axial groove portion 50.1, at its lower end. Inthis piston position, the gas inlet opening 52 disposed in the cylinderwall 8, the overflow openings 53, and the gas outlet opening 54 are allcovered by the outer wall 25 of the piston. The lubricant mixturedelivered via the supply bores 10 can flow via the groove 50 as far asthe through bore 51 during the downward motion of the piston through thegroove 50.

Now in order to reduce the escape of lubricant from the gas outlet 54 toa minimum, care is taken by means of the offset arrangement of thegroove portion 50.2 relative to the groove portion 50.1 that when amiddle piston position is reached, as shown in FIG. 15, the supply bores10 are covered by the outer piston surface 25 over a portion of thepiston stroke, so that during this phase the supply of lubricant to thegroove 50 is interrupted. By means of a corresponding embodiment of thecircumferentially extending groove portion 50.3, in the transitionregion between the upper, axially extending groove portion 50.2 and thegroove portion 50.3, it can now be attained that once the bottom deadcenter position is reached, the transition region 50.5 will cover thesupply bore for a brief period, so that lubricant mixture is brieflysupplied in the region of the turning point. The circumferentiallyextending groove portion 50.3 is disposed with respect to the pistonring 9 such that the covering of the region 50.5 with the supply bore 10does not occur until the circumferentially extending region 50.3 islocated below where it coincides with the outlet conduit 54. As soon asthe piston is again on its upward stroke, the supply bore 10 is quicklyclosed, and the supply of lubricant mixture is interrupted.

As FIG. 15 also shows, the upper, axially extending portion 50.2 of thegroove 50 associated with the gas outlet conduit 54 may be embodied assomewhat longer than the corresponding region on the outer piston wallthat is associated with the gas inlet conduits 52, so the gas outlet onthat side the supply of lubricant mixture takes place over a somewhatlonger period of time.

FIGS. 16 and 17, in a view corresponding to FIGS. 14 and 15, show adifferent embodiment for the groove 50. The structure and mode ofoperation are essentially equivalent to the embodiment of FIGS. 14 and15. However, the difference is that the groove 50 is disposedessentially in a U on the outer piston surface 25, and that two supplybores 10.1 and 10.2 are provided per groove, each supply boredischarging in the lower end region of the axially extending grooveportion 50.1. The through bore 51 that communicates with the interior ofthe piston preferably with the piston pin bearing, is disposed in thisembodiment in the middle region of the circumferentially extendinggroove portion 50.3.

FIG. 18, in an enlarged vertical section, shows an embodiment for theformation and delivery of the lubricant mixture immediately in theregion of the cylinder. Here the supply opening 10 in the cylinder wall8 communicates with an inlet conduit 55 for supplying a gaseous carriermedium, which communicates via corresponding inlet lines with a supplymeans. The inlet conduit 55 has a larger diameter than the supplyopening 10. Introduced into this inlet conduit 55, preferably coaxially,is an inlet tube 56 whose outlet opening 57 discharges in the region ofthe inlet conduit 55 in which the diameter of the inlet conduit 55decreases the diameter of the supply opening 10. The inlet line 56 alsocommunicates with a suitable lubricant supply. As a result, it isattained that by means of the gaseous carrier medium flowing in via theinlet conduit 55, the lubricant emerging from the outlet opening 57 canflow into the interstice defined by the grooves 50 between the cylinderwall 8 and the outer piston surface 25.

FIG. 19 schematically shows a two-stroke internal combustion engine,whose cylinder 8 is provided with an overflow conduit 53 and an outletconduit 54 and which is embodied as a so-called crankcase-scavengedengine. This engine compresses the air in the crankcase 58 in thedownward motion of the piston 7. The compressed air can then flow intothe combustion chamber, at the moment the overflow conduits open, and isfurther compressed in the combustion chamber. The fuel is then injectedand ignited in the usual way via a spark plug, so that the piston 7 canexecute its working stroke in the downward motion. At the end of theworking stroke the outlet conduit 54 is uncovered, so that the combustedexhaust gases are scavenged from the cylinder chamber by the inflowingfresh air.

During the downward motion of the piston 7, an excess pressure iscreated in the crankcase 58; this pressure reaches its maximum at theinstant the overflow conduits open. This pressure pulsation in thecrankcase can now be exploited in order to feed air from the crankcaseinto a conditioning device 1, via an air line 59 in which a check valve60 is disposed; the air is then carried over suitable transport lines 2,as already shown in FIG. 1, to the supply openings 10 for the lubricantmixture. During the upward motion of the piston 7, a negative pressurefor aspirating the fresh air is created in the crankcase 58. In thisphase, a transport of the air then takes place through the transportlines 2 to the various supply openings 10. By way of this air, as shownin FIG. 18, the lubricant supplied via separate inlet lines 56 can beatomized immediately before being introduced into the cylinders.

In the embodiment shown here, it is also possible, however, to embodythe conditioning device 1 as a container, in which the lubricant isatomized via an atomizer 61, so that an oil-air mixture is carried fromthis container through the transport lines 2 to the supply openings 10.As shown in FIG. 1 and described in conjunction with it, the transportlines 2 can also be extended as far as the crankshaft bearing and theconnecting rod bearing, so that these bearings are jointly lubricated aswell.

We claim:
 1. A process for supplying a liquid lubricant to points of areciprocating piston engine which are to be lubricated and which includeat least running surfaces of a piston-cylinder tube unit of thereciprocating piston engine, the reciprocating piston engine having apiston and a cylinder, the process comprising the steps of:uniting thelubricant in at least one conditioning device with a gaseous transportmedium; forming, in the conditioning device, a lubricating mixtureincluding small liquid particles of lubricant carried by the gaseoustransport medium; passing at least one of the lubricating mixture andthe lubricant with the gaseous transport medium through a plurality ofsupply ducts corresponding to the points to be lubricated; and drawingaway, through at least one drain disposed in a region of the points tobe lubricated, the gaseous transport medium and excess lubricant fromthe points to be lubricated.
 2. The process according to claim 1,wherein the step of passing includes the step of dosing the lubricatingmixture for the respective ones of the points to be lubricated byeffecting various flow resistances in the supply ducts correspondingthereto, the various flow resistances corresponding to predetermineddoses of the lubricating mixture.
 3. The process according to claim 2,wherein the step of effecting various flow resistances includes the stepof selecting one of various cross-sectional dimensions and variouscross-sectional geometries of respective outlet openings of the supplyducts.
 4. The process according to claim 1, wherein the step of passingincludes the step of supplying lubricating mixture to the points to belubricated virtually continuously.
 5. The process according to claim 1,wherein the step of passing includes the step of dosing the lubricatingmixture for the respective ones of the points to be lubricated byvarying, between the supply ducts, one of a volumetric flow of thetransport medium and a concentration of the lubricant in the transportmedium.
 6. The process according to claim 1, wherein the step of passingincludes the step of dosing the lubricating mixture for the respectiveones of the points to be lubricated as a function of one of a load andrpm of the reciprocating piston engine.
 7. The process according toclaim 1, wherein the step of passing includes the step of supplyinglubricating mixture to an upper connecting rod bearing of the pistonthrough at least one bore in the piston which cooperates with a supplybore in a wall of the cylinder.
 8. The process according to claim 1,wherein:the step of passing includes the step of supplying lubricatingmixture to the piston through a groove extending on an outer surface ofthe piston; and the step of drawing away includes the step of supplyinglubricating mixture to an upper connecting rod bearing of the piston bydischarging lubricating mixture supplied to the piston through at leastone end of a piston pin boss of the piston through bores in acorresponding piston pin of the piston disposed in a region of the upperconnecting rod bearing.
 9. The process according to claim 1, wherein:atleast one of the points to be lubricated is a surface to be lubricatedonto which a corresponding supply duct discharges; and the step ofpassing includes the step of supplying lubricating mixture as alubricating wall film on the surface to be lubricated.
 10. The processaccording to claim 1, wherein the step of passing includes the step oftransporting the lubricant as a wall film in the supply duct.
 11. Theprocess according to claim 1, wherein the step of passing includes thestep of supplying the lubricating mixture to the points to be lubricatedat excess pressure.
 12. The process according to claim 1, wherein thestep of drawing away includes the step of subjecting the drains tonegative pressure.
 13. An assembly comprising:a reciprocating pistonengine including a piston cylinder tube unit having:a cylinder includinga cylinder wall, the cylinder wall having therein at least one supplybore for supplying lubricant as small liquid particles carried in agaseous transport medium to points of the piston cylinder tube unit tobe lubricated; a piston having an outermost surface, an interior region,a piston bearing disposed in the interior region, an uppermost pistonring and a lowermost piston ring, the piston rings being disposed in acircumferential direction about the outermost surface of the piston, thepiston being disposed in the cylinder such that it defines an intersticebetween its outermost surface and the cylinder wall and further beingadapted to move axially between a bottom dead center position and a topdead center position, the supply bore in the cylinder wall beingdisposed such that it discharges lubricant into the interstice and belowthe uppermost piston ring when the piston is in its bottom dead centerposition, the outermost surface of the piston further including: atleast one groove having:at least one axial groove portion extending, ata region beginning at a lower end of the piston, essentially in an axialdirection of the piston, the axial groove further including:a bottom enddisposed at the lower end of the piston such that the supply boredischarges lubricant into the bottom end when the piston is at itsbottom dead center position; a lower end portion extending axiallyupward from the bottom end; and an upper end portion adjoining andcircumferentially offset with respect to the lower end portion suchthat, during a downward axial movement of the piston before bottom deadcenter is reached, the supply bore does not communicate with the upperend portion and is covered by the outermost surface of the piston over apredetermined range of the axial movement of the piston; acircumferential groove portion adjoining the axial groove portion andextending in the circumferential direction of the piston below thelowermost piston ring; and a transition groove portion disposed betweenand adjoining both the upper end portion and the circumferential grooveportion; and a draining means for draining the lubricant away from thepoints of the piston cylinder tube unit to be lubricated, the drainingmeans including a venting bore communicating with the circumferentialgroove portion and discharging lubricant into the piston bearingdisposed in the interior region of the piston; anda means for supplyingliquid lubricant to the reciprocating piston engine, the means beingoperatively connected to the reciprocating piston engine and includingmeans for transporting the liquid lubricant to the supply bore of thepiston cylinder tube unit.
 14. The assembly according to claim 13,wherein the transition groove portion is disposed on the outermostsurface of the piston such that the supply bore discharges lubricanttherein when the piston is at its bottom dead center position.
 15. Theassembly according to claim 13, wherein:the at least one axial grooveportion includes two axial groove portions disposed on the outermostsurface of the piston and adjoined by the circumferential groove portionsuch that the at least one groove is essentially U-shaped; and the atleast one supply bore includes two supply bores discharging into thebottom end of each of the two axial groove portions, respectively. 16.The assembly according to claim 13, wherein:the reciprocating pistonengine is a two-stroke internal combustion engine; the cylinder wallincludes an inlet slit and an outlet slit spaced with respect to oneanother in a circumferential direction; and the supply bores aredisposed between the inlet slit and the outlet slit such that they arebelow the uppermost piston ring when the piston is in its bottom deadcenter position.
 17. The assembly according to claim 13, wherein:thepiston bearing includes an upper connecting rod bearing; the pistonfurther includes:a piston pin boss disposed adjacent the upperconnecting rod bearing; a piston pin disposed in the piston pin boss andhaving at least one bore extending therein is a radial direction withrespect to the piston and communicating with the upper connecting rodbearing; and the at least one groove discharges into the at least onebore extending through the piston pin for supplying lubricant to theupper connecting rod bearing.
 18. The assembly according to claim 13,wherein:the piston bearing includes an upper connecting rod bearing; andthe piston further includes at least one bore therein communicating withthe upper connecting rod bearing and extending from the outermostsurface of the piston such that it communicates with the supply bore ata predetermined axial position of the piston.
 19. The assembly accordingto claim 13, wherein the supply bore is adapted to carry liquidlubricant therein as a wall film of lubricant on walls thereof, the wallfilm being entrained by the gaseous transport medium flowing through thesupply bore, the supply bore further including a cross-sectionalconstriction therein disposed immediately upstream of the points to belubricated, the constriction being configured such that a wall film oflubricant develops on the cylinder wall when the supply bore dischargeslubricant thereto.
 20. The assembly according to claim 13, wherein thecylinder wall further includes:a first supply line for the gaseoustransport medium, the first supply line communicating with the supplybore; and a second supply line for the liquid lubricant, the secondsupply line discharging into the first supply line at a distanceupstream of the supply bore.
 21. The assembly according to claim 13,wherein the supply bore includes a cross-sectional constriction thereindisposed immediately upstream of the points to be lubricated, theconstriction being adapted to deflect a flow of small liquid particlesof lubricant carried by the gaseous transport medium.
 22. The assemblyaccording to claim 13, wherein:the piston has a compression side and acounterpressure side; and the supply bore is disposed on at least one ofthe compression side and the counterpressure side of the piston.
 23. Theassembly according to claim 21, wherein the constriction consists of aporous body adapted to deflect the flow of the small liquid particlessuch that the particles grow in size inside the constriction.